Mapping:
Demars et al. (2013) conducted a GWAS by genotyping 28 hyper-prolific and 11 control French Grivette ewes with the Illumina OvineSNP50 chip. A single region on the X chromosome, including the prolificacy gene BMP15, was highlighted. BMP15 was thus a highly likely positional candidate gene.

Molecular basis:
Following the results described in the Mapping section, sequencing of BMP15 revealed six polymorphisms, one of which (950C>T; T317I) was strongly associated with fecundity. Genotyping of this polymorphism in additional randomly chosen ewes confirmed the effect, with TT homozygotes having an average ovulation rate of 4.58 compared with 2.94 for CT and 2.53 for CC ewes, with corresponding averages for litter size being 2.50 for TT, 1.93 for CT and 1.83 for CC (Demars et al., 2013). Interestingly, the authors note that the high fecundity of homozygous mutant (TT) ewes is "in striking contrast with the sterility exhibited by all other known homozygous BMP15 mutations".

Control:
Even though this trait is not regarded as a disorder, it is worth noting that in some situations, farmers prefer to not have prolific ewes. The discovery of the DNA basis of this form of prolificacy should enable breeders to better plan matings so as to avoid producing such ewes. (text written by FN, with thanks to Julie Demars)

Variants

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